Switchgear of that type is known in particular from European Patent Application EP A 0 567 773. The moving contact of the disconnector is organized to occupy a third position in which it connects the generator to the transformer via the fixed pole when the circuit breaker is closed. In the third position, the moving contact withstands electric current of a magnitude specific to the steady conditions of the generator, while, in the first and second positions, when the circuit breaker is open, the moving contact withstands electric current of a magnitude specific to the transient conditions of the generator during starting or during grounding. The moving contact is organized to withstand both types of electric current conditions, which means that the size and the cost of the moving contact are problematic.